The Sun deposits 120,000 terawatts (TW) of power onto the Earth's surface. This is more than the 13 TW of total power that is currently used by the planet's population. Photovoltaics (PV) convert solar energy into direct current electricity using semiconducting materials that exhibit the photovoltaic effect. The photovoltaic effect includes photons of light exciting electrons into a higher state of energy, allowing them to act as charge carriers for an electric current. A photovoltaic system can employ solar panels including a number of solar cells to supply usable solar power.